(1) Field of the Invention
The present invention relates in general to V-type internal combustion engines and more particularly to a cast one-piece crankcase and cylinder block construction for such engines.
(2) Description of the Prior Art
In the prior art relating to internal combustion engines it has been common to construct V-type engines from a cast crankcase and a separate cylinder assembly which is assembled onto the crankcase by bolts. Usually, casting produces a crankcase opened at its bottom side wall, and the opening of the crankcase is later closed with a side wall which is formed by a separate process of casting. To install a crankshaft, a bore is drilled in the end wall of the crankcase, sized to a larger diameter than the crankshaft webs so that the crankshaft can be inserted into position inside the crankcase through the bore. After the insertion, the drilled bore is filled to a smaller diameter enough to fittingly carry the end bearing supporting the end of the crankshaft. Thus, not only have the entire assembling operation of an engine demanded considerable manpower and time but also the structure required to support the end bearing in the end wall bore have resulted in increasing the overall weight of the crankcase.
Furthermore, because of the design requirement that the crankcase first comes without its bottom side wall, the cylinder block has to be later made integral with the crankcase, adding an extra amount of labor and with a resultant increase of weight from the attaching devices employed to put them together.
The reason for the unavailability of a one-piece crankcase and cylinder block casting is largely attributable to the limited capacities of the conventional casting machines. In casting, the cores are pulled out from the crankcase in a direction that is substantially perpendicular to the axis of the crankshaft and so are the cores from the cylinder block. To make a one-piece crankshaft and cylinder block, the molding machine has to be impractically large enough to achieve this pulling over a sum distance for the cores from the crankcase and those for the cylinder block.
Another problem with the conventional V-type engine designs is that a gear case has to be mounted externally of the crankcase to house the cam gear, which also added extra machining and assembling operations to the entire crankcase buildup.
It is this situation that gave rise to the present invention.